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United States Patent |
5,506,553
|
Makita
,   et al.
|
April 9, 1996
|
High-frequency filter
Abstract
One example of a high-frequency filter includes a dielectric substrate
having a high dielectric constant. On one whole main face of the
dielectric substrate, an earth electrode is formed. On the other main face
of the dielectric substrate, two pattern electrodes are formed. The
pattern electrodes have first parts formed in parallel at an interval, and
second parts extended in crossing (non-parallel) directions. Also, on one
main face of the dielectric substrate, input-output electrodes are
respectively formed near the end parts of the pattern electrodes, and
capacitors are respectively formed between the open end parts and the
input-output electrodes.
Inventors:
|
Makita; Takashi (Nagaokakyo, JP);
Sasaki; Yutaka (Nagaokakyo, JP);
Kaneko; Toshimi (Nagaokakyo, JP)
|
Assignee:
|
Murata Manufacturing Co., Ltd. (JP)
|
Appl. No.:
|
324905 |
Filed:
|
October 18, 1994 |
Foreign Application Priority Data
| Oct 22, 1993[JP] | 5-287512 |
| Nov 09, 1993[JP] | 5-304839 |
Current U.S. Class: |
333/204; 333/238 |
Intern'l Class: |
H01P 001/203 |
Field of Search: |
333/204,205,238,246
|
References Cited
U.S. Patent Documents
3016497 | Jan., 1962 | Kostelnick | 333/204.
|
4074214 | Feb., 1978 | Aichholzer | 333/204.
|
4488130 | Dec., 1984 | Young et al. | 333/246.
|
4489292 | Dec., 1984 | Ogawa | 333/246.
|
5313662 | May., 1994 | Ooi et al. | 333/204.
|
Foreign Patent Documents |
63404 | Mar., 1993 | JP | 333/204.
|
Primary Examiner: Gensler; Paul
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb & Soffen
Claims
We claim:
1. A high-frequency filter comprising:
a dielectric substrate;
an earth electrode formed on one main face of said dielectric substrate;
and
plural pattern electrodes formed on the other main face of said dielectric
substrate so as to be opposite to said earth electrode,
wherein first parts of said plural pattern electrodes are formed
substantially in parallel and separated by an interval,
second parts of said plural pattern electrodes having first and open ends
are formed so as to extend away from said first parts at their first ends
in non-parallel directions, and
a non-magnetic dielectric layer is formed so as to provide a capacitance at
an overlap between the second parts of said plural pattern electrodes.
2. A high-frequency filter according to claim 1, wherein a further
capacitance is formed between respective open ends of said plural pattern
electrodes.
3. A high-frequency filter according to claim 1, wherein each said pattern
electrode forms a quarter-wave resonator.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-frequency filter, and particularly,
to a high-frequency filter which is a plane type distributed constant
filter using a dielectric substrate and having plural resonators and is
used as, for example, a band-pass filter or the like.
2. Description of the Prior Art
FIG. 18 is a plan view showing an example of a conventional high-frequency
filter which is in the background of the present invention, FIG. 19 is a
side view thereof. The high-frequency filter 1 includes a dielectric
substrate 2 having, for example, a dielectric constant of 10-20. On one
whole main face of the dielectric substrate 2, an earth electrode 3 is
formed. Also, on the other main face of the dielectric substrate 2, two
linear pattern electrodes 4a and 4b are formed so as to be opposite to the
earth electrode 3. In this case, the pattern electrodes 4a and 4b are
formed in parallel at a fixed interval S1 so as to electromagnetically
couple. One end of each of the pattern electrodes 4a and 4b is connected
to the earth electrode 3 via one side face of the dielectric substrate 2.
One resonator of length .lambda./4 is constructed with the dielectric
substrate 2, the earth electrode 3 and one pattern electrode 4a, and
another resonator of length .lambda./4 is constructed with the dielectric
substrate 2, the earth electrode 3 and the other pattern electrode 4b.
Also, input-output electrodes 5a and 5b are formed so as to extend from
intermediate parts of the pattern electrodes 4a and 4b to both side parts
of the dielectric substrate 2. Thus, the high-frequency filter 1 is
constructed as a comb line filter.
FIG. 20 is a plan view showing another example of a conventional
high-frequency filter which is in the background of the present invention.
In the conventional example shown in FIG. 20, compared with the
conventional example shown in FIG. 18 and FIG. 19, the opposite ends of
the pattern electrodes 4a and 4b are connected to the earth electrode 3.
Thus, the high-frequency filter 1 shown in FIG. 20 is constructed as an
interdigital filter.
Also, for example, Japanese publication No. 28441/1985 discloses an example
of a conventional strip line filter which is in the background of the
present invention. FIG. 21 is a plan view showing an example of such a
conventional high-frequency filter, FIG. 22 is a side view thereof. The
high-frequency filter 1 shown in FIG. 21 and FIG. 22 includes a dielectric
substrate 2 having, for example, a dielectric constant of 10-20. On one
whole main face of the dielectric substrate 2, an earth electrode 3 is
formed. Also, on the other main face of the dielectric substrate 2, five
linear pattern electrodes 4a, 4b, 4c, 4d and 4e are formed so as to be
opposite to the earth electrode 3. In this case, the pattern electrodes
4a-4e are formed in parallel at a fixed interval S1 so as to
electromagnetically couple each two adjoining pattern electrodes. One end
of each of the pattern electrodes 4a-4e is connected to the earth
electrode 3 via one side face of the dielectric substrate 2. Thus, five
resonators of length .lambda./4 are constructed with the dielectric
substrate 2, the earth electrode 3 and the five pattern electrodes 4a-4e.
Also, input-output electrodes 5a and 5b are formed so as to extend from
intermediate parts of the pattern electrodes 4a and 4e to both sides of
the dielectric substrate 2. Thus, the high-frequency filter 1 is
constructed as a comb line filter.
In the high-frequency filter 1 shown in FIG. 18 through FIG. 20, for
miniaturizing the filter as required in recent years, when the dielectric
constant of the dielectric substrate 2 is increased for shortening each
length L1 of the pattern electrodes 4a and 4b of the two resonators and so
on, an interference effect in an electromagnetic field between the two
resonators is too strong. That is, when the dielectric constant of the
dielectric substrate 2 is increased, the electromagnetic coupling between
the pattern electrodes 4a and 4b of the two resonators is too strong.
Thus, frequency characteristics such a selectivity characteristic of the
high-frequency filter are deteriorated. For correcting the deterioration
of the frequency characteristics, it is necessary to redesign it for
extending the interval S1 between the pattern electrodes 4a and 4b of the
two resonators and so on. However, when the interval S1 between the
pattern electrodes 4a and 4b of the two resonators is extended, the
high-frequency filter becomes large, not miniaturized.
Also, in the high-frequency filter 1 shown in FIG. 18 through FIG. 20,
since its input-output impedance and an external circuit are matched by
drawing the input-output electrodes 5a and 5b from the intermediate parts
of the pattern electrodes 4a and 4b directly, the coupling degree between
the two resonators is changed by an interference effect in an
electromagnetic field, so it is necessary to adjust each distance D1 from
the short ends (the ends connected to the earth electrode 3) of the
pattern electrodes 4a and 4b to the input-output electrodes 5a and 5b, or
each width T of the input-output electrodes 5a and 5b, which makes such a
filter complex and difficult to design.
Furthermore, in the high-frequency filter 1 shown in FIG. 18 through FIG.
20, there is a problem that even if the input-output impedance is matched
as above mentioned, when the impedance of the external circuit is changed,
the frequency characteristic is easily changed too.
Also, in the high-frequency filter 1 shown in FIG. 21 and FIG. 22, for
obtaining a high efficiency frequency characteristic having a large
attenuation, it is a problem that not only must the resonators be coupled
to form a multi-stage filter, which makes the filter large, but also it
becomes difficult, involving an exponential function, to design in order
to increase the stage number of the resonators.
Furthermore, in the high-frequency filter 1 shown in FIG. 21 and FIG. 22,
for miniaturizing the filter as the market has required in recent years,
when the dielectric constant of the dielectric substrate 2 is increased
for shortening each length L1 of the pattern electrodes 4a-4e of the five
resonators and so on, an interference effect in an electromagnetic filed
between each two adjoining resonators is too strong. Thus, frequency
characteristics such as a selectivity characteristic of the high-frequency
filter are deteriorated. For correcting the deterioration of the frequency
characteristics, a redesign is necessary for extending the interval S1
between the pattern electrodes of each two adjoining resonators and so on.
Then, when the interval S1 between the pattern electrodes of two adjoining
resonators is extended, the high-frequency filter becomes large, which
interferes with miniaturizing, and it becomes difficult to design it. In
some cases, it is impossible to design it.
SUMMARY OF THE INVENTION
Therefore, it is a primary object of the present invention to provide a
high-frequency filter that can be miniaturized.
A high-frequency filter according to the present invention is a
high-frequency filter comprising a dielectric substrate having a high
dielectric constant, an earth electrode formed on one main face of the
dielectric substrate, and plural pattern electrodes formed on the other
main face of the dielectric substrate so as to be opposite to the earth
electrode, wherein first parts of the plural pattern electrodes are formed
in parallel separated by an interval, and second parts of the plural
pattern electrodes are formed so as to extend in crossing (non-parallel)
directions.
In the high-frequency filter according to the present invention, plural
resonators are formed by the dielectric substrate, the earth electrode and
the plural pattern electrodes.
Also, since the first parts of the plural pattern electrodes are formed in
parallel at an interval, the plural pattern electrodes are
electromagnetically coupled at the first parts. However, since the second
parts of the plural pattern electrodes are formed so as to extend in
crossing directions, the plural pattern electrodes are hardly
electromagnetically coupled at the second parts. Thus, the plural
resonators hardly have any electromagnetic interference effect.
According to the present invention, in a high-frequency filter, since a
dielectric substrate having a high dielectric constant is used, the length
of each of the plural pattern electrodes can be shortened, and
furthermore, since the plural resonators have hardly any interference
effect in an electromagnetic field, the interval between the pattern
electrodes of the plural resonators can be narrowed. Thus, it is possible
to miniaturize the high-frequency filter.
It is another object of the present invention to provide a high-frequency
filter which can be miniaturized and has a good frequency characteristic.
Another high-frequency filter according to the present invention is a
high-frequency filter comprising a dielectric substrate, an earth
electrode formed on one main face of the dielectric substrate, and plural
pattern electrodes formed on the other main face of the dielectric
substrate so as to be opposite to the earth electrode, wherein first parts
of the plural pattern electrodes are formed in parallel at an interval,
second parts of the plural pattern electrodes are formed so as to extend
in crossing directions, and a dielectric layer is formed between
overlapped parts of the second parts of the plural pattern electrodes.
Further, an electrostatic capacitance may be formed between two
input-output electrodes.
In this high-frequency filter, plural resonators are formed by the
dielectric substrate, the earth electrode and the plural pattern
electrodes.
Since the dielectric layer is formed between the overlapped parts of the
second parts of the plural pattern electrodes, and an electrostatic
capacitance is generated therebetween, not only an electromagnetic
coupling, but also a capacitive coupling is generated between the plural
pattern electrodes. Thus, the interval between the plural pattern
electrodes can be extended for decreasing the coupling. Accordingly, in
addition to the effect of overlapping the second parts of the plural
pattern electrodes, the distance in the line direction of the plural
pattern electrodes can be shortened.
According to the present invention, in a high-frequency filter, the
distance in the line direction of the plural pattern electrodes can be
shortened. Thus, it is possible to miniaturize a high-frequency filter.
Further, when a dielectric substrate having a high dielectric constant is
used, the length of each of the plural pattern electrodes can be shortened
and more miniaturized, whereby the effects of the present invention become
even more preferable.
Furthermore, according to the present invention, in a high-frequency
filter, since the dielectric layer is formed between the overlapped parts
of the second parts of the plural pattern electrodes, and the
electrostatic capacitance is generated therebetween, an attenuation pole
is generated at a low frequency side of a passband, improving the
frequency characteristic. Further, when electrostatic capacitance is
formed between two input-output electrodes in the high-frequency filter,
attenuation poles are generated at both a high frequency side and a low
frequency side of a passband, whereby the frequency characteristic becomes
even better.
The above and further objects, features and advantages of the present
invention will be more fully apparent from the following detailed
description of the embodiments with accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view showing one embodiment of the present invention.
FIG. 2 is a side view of the embodiment shown in FIG. 1.
FIG. 3 is a sectional view taken along the line III--III of FIG. 1.
FIG. 4 is an equivalent circuit diagram of the embodiment shown in FIG. 1.
FIG. 5 is a plan view showing a modification of the embodiment shown in
FIG. 1.
FIG. 6 is a sectional view taken along the line VI--VI of FIG. 5.
FIG. 7 is a plan view showing another modification of the embodiment shown
in FIG. 1.
FIG. 8 is a sectional view taken along the line VIII--VIII of FIG. 7.
FIG. 9 is a plan view showing another embodiment of the present invention.
FIG. 10 is a sectional view taken along the line X--X of FIG. 9.
FIG. 11 is sectional view taken along the line XI--XI of FIG. 9.
FIG. 12 is an equivalent circuit diagram of the embodiment shown in FIG. 9.
FIG. 13 is a plan view showing still another embodiment of the present
invention.
FIG. 14 is an equivalent circuit diagram of the embodiment shown in FIG.
13.
FIG. 15 is a graph showing frequency characteristics of the embodiment
shown in FIG. 9 and the embodiment shown in FIG. 13.
FIG. 16 is an illustrative view showing a modification of the embodiment
shown in FIG. 9.
FIG. 17 is an illustrative view showing another modification of the
embodiment shown in FIG. 9.
FIG. 18 is a plan view showing an example of a conventional high-frequency
filter which is a background of the present invention.
FIG. 19 is a side view of the high-frequency filter shown in FIG. 18.
FIG. 20 is a plan view showing another example of a conventional
high-frequency filter which is a background of the present invention.
FIG. 21 is a plan view showing still another example of a conventional
high-frequency filter.
FIG. 22 is a side view of the high-frequency filter shown in FIG. 21.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a plan view showing one embodiment of the present invention, FIG.
2 is a side view thereof, and FIG. 3 is a sectional view taken along the
line III--III of FIG. 1. The high-frequency filter 10 includes, for
example, a rectangular dielectric substrate 12. A material having a high
dielectric constant, for example, a dielectric constant of 50, is used as
the dielectric substrate 12.
On one whole main face of the dielectric substrate 12, an earth electrode
14 is formed. The earth electrode 14 is also extended onto an end part of
the other main face of the dielectric substrate 12.
On a second main face of the dielectric substrate 12, two pattern
electrodes 16a and 16b are formed. One pattern electrode 16a has a first
part 18a linearly extending from the earth electrode 14 in the front and
rear direction of the substrate, and a second part 20a linearly extending
from the first part 18a in a direction toward the outside of the substrate
at an angle, for example, 45 degrees. Similarly, the other pattern
electrode 16b has a first part 18b linearly extending from the earth
electrode 14 in the front and rear direction, and a second part 20b
linearly extending from the first part 18b in an outward direction at an
angle, for example, 45 degrees. Thus, in the two pattern electrodes 16a
and 16b, the first parts 18a and 18b are formed in parallel at an interval
S2, and the second parts 20a and 20b are formed so as to extend in
crossing (non-parallel) directions. Thus, the two pattern electrodes 16a
and 16b are electromagnetically coupled at the first parts 18a and 18b,
and are hardly electromagnetically coupled at the second parts 20a and
20b.
Furthermore, on the second main face of the dielectric substrate 12, two
input-output electrodes 24a and 24b are formed near the tip parts (the
open ends) 22a and 22b of the pattern electrodes 16a and 16b.
Also, capacitors 26a and 26b are respectively formed between the tip parts
22a, 22b of the pattern electrodes 16a, 16b and the input-output
electrodes 24a and 24b. As shown in FIG. 3, one capacitor 26a is formed by
the tip part 22a of the pattern electrode 16a, a dielectric layer 28a
formed on the tip part 22a and so on, and an electrode 30a extending from
the input-output electrode 24a to the top of the dielectric layer 28a.
Similarly, the other capacitor 26b is formed by the tip part 22b of the
pattern electrode 16b, a dielectric layer 28b formed on the tip part 22b
and so on, and an electrode 30b extending from the input-output electrode
24b to the top of the dielectric layer 28b.
Accordingly, the high-frequency filter 10 has an equivalent circuit shown
in FIG. 4.
In the high-frequency filter 10, one resonator of length .lambda./4 is
constructed with the dielectric substrate 12, the earth electrode 14 and
one pattern electrode 16a, another resonator of length .lambda./4 is
constructed with the dielectric substrate 12, the earth electrode 14 and
the other pattern electrode 16b.
Also, in the high-frequency filter 10, since the first parts 18a and 18b of
the two pattern electrodes 16a and 16b are formed in parallel at the
interval $2, the two pattern electrodes 16a and 16b are
electromagnetically coupled at the first parts 18a and 18b. However, since
the second parts 20a and 20b of the two pattern electrodes 16a and 16b are
formed so as to extend in crossing directions, the two pattern electrodes
16a and 16b are hardly electromagnetically coupled at the second parts 20a
and 20b. Thus, the two resonators hardly have any interference effect in
an electromagnetic field.
In the high-frequency filter 10, since the dielectric substrate 12 has a
high dielectric constant, the length of each of the two pattern electrodes
16a and 16b can be shortened in comparison to each length in the
conventional example, and furthermore, since the two resonators hardly
have any interference effect in an electromagnetic field, the interval $2
between the pattern electrodes 16a and 16b of the two resonators can be
narrowed in comparison to the interval S1 in the conventional example.
Thus, in the high-frequency filter 10, it is possible to make the filter
smaller than the conventional example.
Also, in the high-frequency filter 10, since the two resonators are coupled
mainly by electromagnetic coupling at only the first parts 18a and 18b
near the 10 short proximal ends of the pattern electrodes 16a and 16b of
the two resonators, and the two resonators hardly have any interference
effect in an electromagnetic field, regardless of using the dielectric
substrate 12 having a high dielectric constant, complexity or difficulty
in design is rare, so it is comparatively easy to design.
Furthermore, in the high-frequency filter 10, since the input-output
electrodes 24a and 24b are connected to the pattern electrodes 16a and 16b
of the two resonators via the capacitors 26a and 26b, it is possible to
have a comparatively high input-output impedance, for example, one hundred
and several tens of ohms. Thus, in the high-frequency filter 10, against
the impedance changing of the external circuit having a nominal impedance
of 50 ohms, the deterioration of the frequency characteristic is small.
Also, the high-frequency filter 10 has some degree of freedom in design, as
the distance L2 from the end of the earth electrode 14 on the second main
face of the dielectric substrate 12 to the 45 degree corner of the pattern
electrodes 16a and 16b, or the interval $2 between the first parts 18a and
18b of the pattern electrodes 16a and 16b, can be suitably changed.
Further, the position spacing D2 of the input-output electrodes 24a and
24b can be changed to some extent without substantially changing the
.lambda./4 length of the resonator. That is, handling becomes easy in case
of mounting the high-frequency filter on a printed circuit board or the
like.
FIG. 5 is a plan view showing a modification of the embodiment shown in
FIG. 1, FIG. 6 is a sectional view taken along the line VI--VI of FIG. 5.
The main difference between the embodiment shown in FIG. 5 and FIG. 6, and
the embodiment shown in FIG. 1, is that chip capacitors 26a and 26b are
connected between the tip parts 22a, 22b of the pattern electrodes 16a,
16b and the input-output electrodes 24a and 24b.
FIG. 7 is a plan view showing another modification of the embodiment shown
in FIG. 1, FIG. 8 is a sectional view taken along the line VIII--VIII of
FIG. 7. The main difference between the embodiment shown in FIG. 7 and
FIG. 8, and the embodiment shown in FIG. 1, is that the tip parts 22a and
22b of the pattern electrodes 16a and 16b and the input-output electrodes
24a and 24b are formed close together. Thus, the capacitances of the
capacitors 26a and 26b formed by the gap between the tip parts 22a, 22b of
the pattern electrodes 16a, 16b and the input-output electrodes 24a, 24b,
are respectively used.
Meanwhile, in each embodiment shown in FIG. 1 through FIG. 8, though the
second parts 20a and 20b of the pattern electrodes 16a and 16b are
respectively formed extending from the first parts 18a and 18b at an angle
of 45 degrees, it is sufficient merely to form the second parts 20a and
20b extending in crossing directions, so the second parts 20a and 20b may
be formed at another angle. For example, one angle may be 40 degrees and
the other angle may be 50 degrees.
Also, in each embodiment shown in FIG. 1 through FIG. 8, though having two
pattern electrodes, that is, two resonators of length .lambda./4, the
present invention can also be applied to a high-frequency filter having
three pattern electrodes, that is, three resonators of length .lambda./4
in this case, the pattern electrodes may be formed so that the second
parts (the open ends) are extended in crossing directions in each two
adjoining pattern electrodes.
Meanwhile, in each embodiment shown in FIG. 1 through FIG. 8, though in
each example, each resonator has a length of .lambda./4 having the first
end connected to the earth electrode, the present invention is also
applicable to a high-frequency filter using resonators of length
.lambda./2 having the first end open.
Furthermore, in each embodiment shown in FIG. 1 through FIG. 8, though one
dielectric substrate is used, the present invention is also applicable to
a multilayer high-frequency filter wherein plural dielectric layers and so
on are laminated and made uniform. In this case, since the coupling
between the pattern electrodes becomes strong, the present invention
becomes especially useful.
FIG. 9 is a plan view showing another embodiment of the present invention,
FIG. 10 is a sectional view taken along the line X--X of FIG. 9. FIG. 11
is a sectional view taken along the line XI--XI of FIG. 9. The
high-frequency filter 10 shown in FIG. 9 includes, for example, a
rectangular dielectric substrate 12. A material having a high dielectric
constant, for example, a dielectric constant of 50 or more, is used as the
dielectric substrate 12.
On one whole main face of the dielectric substrate 12, an earth electrode
14 is formed. The earth electrode 14 is also extended across one side face
and onto an end part of the second main face of the dielectric substrate
12.
On the second main face of the dielectric substrate 12, two pattern
electrodes 16a and 16b are formed. One pattern electrode 16a has a first
part 18a linearly extending from the earth electrode 14 in the front and
rear direction, and a second part 20a linearly extending from the first
part 18a in an inward direction 10 at an angle, for example, 48 degrees.
Similarly, the other pattern electrode 16b has a first part 18b linearly
extending from the earth electrode 14 in the front and rear direction, and
a second part 20b linearly extending from the first part 18b in an inward
direction at an angle, for example, 45 degrees. In this case, in the two
pattern electrodes 16a and 16b, the first parts 18a and 18b are formed in
parallel at an interval $3, and the second parts 20a and 20b are formed so
as to cross each other. Thus, the two pattern electrodes 16a and 16b are
electromagnetically coupled at the first parts 18a and 18b, and are hardly
electromagnetically coupled at the second parts 20a and 20b. Meanwhile,
the tip parts (the open end parts) 22a and 22b of the pattern electrodes
16a and 16b are formed so as to be at opposite sides of the dielectric
substrate 12.
Also, a capacitor 23 is formed between overlapped parts of the second parts
20a and 20b of the pattern electrodes 16a and 16b. As shown in FIG. 10,
the capacitor 23 is formed by an intermediate part of the second part 20a
of the pattern electrode 16a, a dielectric layer 23a formed on the
intermediate part and so on, and an intermediate part of the second part
20b of the pattern electrode 16b formed on the dielectric layer 23a.
Meanwhile, the dielectric layer 23a is formed, for example, of a
dielectric material such as polyimide, for example 5 .mu.m thick, by a
method such as photolithography. Then, between the intermediate parts of
the other side parts 20a and 20b, an electrostatic capacitance Cc, for
example, 0.2-0.8 pF, is generated.
Furthermore, on the second main face of the dielectric substrate 12, two
input-output electrodes 24a and 24b are formed near the tip parts 22a and
22b of the pattern electrodes 16a and 16b.
Also, capacitors 26a and 26b are respectively formed between the tip parts
22a, 22b of the pattern electrodes 16a, 16b and the input-output
electrodes 24a and 24b. As shown in FIG. 11, one capacitor 26a is
constructed with the tip part 22a of the pattern electrode 16a, a
dielectric layer 28a formed on the tip part 22a and so on, and an
electrode 30a extending from the input-output electrode 24a to the top of
the dielectric layer 28a. Similarly, the other capacitor 26b is
constructed with the tip part 22b of the pattern electrode 16b, a
dielectric layer 28b formed on the tip part 22b and so on, and an
electrode 30b extending from the input-output electrode 24b to the top of
the dielectric layer 28b.
Accordingly, the high-frequency filter 10 shown in FIG. 9 has an equivalent
circuit shown in FIG. 12.
In the high-frequency filter 10 shown in FIG. 9, one resonator of length
.lambda./4 is constructed with the dielectric substrate 12, the earth
electrode 14 and one pattern electrode 16a, another resonator of length
.lambda./4 is constructed with the dielectric substrate 12, the earth
electrode 14 and the other pattern electrode 16b.
Also, in the high-frequency filter 10 shown in FIG. 9, since the first
parts 18a and 18b of the two pattern electrodes 16a and 16b are formed in
parallel at the interval $3, the two pattern electrodes 16a and 16b are
electromagnetically coupled at the first parts 18a and 18b. However, since
the second parts 20a and 20b of the two pattern electrodes 16a and 16b are
formed so as to cross each other, the two pattern electrodes 16a and 16b
are hardly electromagnetically coupled at the second parts 20a and 20b.
Thus, the two resonators hardly have any interference effect in an
electromagnetic field.
Furthermore, in the high-frequency filter 10 shown in FIG. 9, since the
dielectric layer 23a is formed between the overlapped parts of the second
part 20a and 20b of the two pattern electrodes 16a and 16b, and the
electrostatic capacitance Cc is generated therebetween, besides an
electromagnetic coupling, a capacitive coupling is generated between the
two pattern electrodes 16a and 16b. Thus, the electromagnetic coupling
must be decreased by extending the interval between the two pattern
electrodes 16a and 16b. Accordingly, besides the effect of overlapping the
second parts 20a and 20b of the two pattern electrodes 16a and 16b, the
distance in the line direction of the two pattern electrodes 16a and 16b
can be drastically shortened by extending the interval between the two
pattern electrodes 16a and 16b, compared with the conventional examples
shown in FIG. 18 through FIG. 22 and the embodiments shown in FIG. 1
through FIG. 8.
As mentioned above, in the high-frequency filter 10 shown in FIG. 9, since
the dielectric substrate 12 having a high dielectric constant is used, the
length of each of the two pattern electrodes 16a and 16b can be shortened
in comparison with each length in the conventional examples shown in FIG.
18 through FIG. 22. Furthermore, the distance in the line direction of the
two pattern electrodes 16a and 16b can be drastically narrowed, in
comparison with the distance in the conventional examples shown in FIG. 18
through FIG. 22 and the embodiments shown in FIG. 1 through FIG. 8. Thus,
in the high-frequency filter 10 shown in FIG. 9, it is possible to
miniaturize more than in the conventional example and so on.
Furthermore, in the high-frequency filter 10 shown in FIG. 9, since the
dielectric layer 23a is formed between the crossing parts of the second
parts 20a and 20b of the two pattern electrodes 16a and 16b, and the
electrostatic capacitance Cc is generated therebetween, an attenuation
pole is generated in a low frequency side, whereby the frequency
characteristic becomes better.
Also, in the high-frequency filter 10 shown in FIG. 9, since the two
resonators are coupled mainly by electromagnetic coupling at only the
first parts 18a and 18b near the short ends of the pattern electrodes 16a
and 16b of the two resonators, and the two resonators hardly have any
interference effect in an electromagnetic field, regardless of the
dielectric substrate 12 having a high dielectric constant, complexity or
difficulty in design is rare, whereby it is comparatively easy to design.
Furthermore, in the high-frequency filter 10 shown in FIG. 9, since the
input-output electrodes 24a and 24b are connected to the pattern
electrodes 16a and 16b of the two resonators via the capacitors 26a and
26b, it is possible to have a comparatively high input-output impedance,
for example, one hundred and several tens of ohms. Thus, in the
high-frequency filter 10 shown in FIG. 9, against the impedance changing
of the external circuit having a nominal impedance of 50 ohms, the
deterioration of the frequency characteristic is small.
Also, in the high-frequency filter 10 shown in FIG. 9, there is some degree
of freedom in design, as the distance L3 from the end of the earth
electrode 14 on the second main face of the dielectric substrate 12 to the
45 degree corner parts of the pattern electrodes 16a and 16b or the
interval $3 between the first parts 18a and 18b of the pattern electrodes
16a and 16b can be suitably changed, and the position spacing D3 of the
input-output electrodes 24a and 24b can be changed to some extent in a
state wherein the .lambda./4 length of the resonator is hardly changed.
FIG. 13 is a plan view showing still another embodiment of the present
invention. In the embodiment shown in FIG. 13, compared with the
embodiment shown in FIG. 9, the tip parts 22a and 22b of the two pattern
electrodes 16a and 16b are formed at the opposite side of the dielectric
substrate 12 from the earth electrode 14. Furthermore, the two
input-output electrodes 24a and 24b are formed close to each other. Thus,
electrostatic capacitance Cp is generated between the two input-output
electrodes 24a and 24b. Accordingly, the high-frequency filter 10 shown in
FIG. 13 has an equivalent circuit shown in FIG. 14.
In the high-frequency filter 10 shown in FIG. 13, compared with the
high-frequency filter 10 shown in FIG. 9, since the electrostatic
capacitance Cp is generated between the two input-output electrodes 24a
and 24b, an attenuation pole is generated at both a low frequency side and
a high frequency side, whereby the frequency characteristic becomes
better.
Also, in the high-frequency filter 10 shown in FIG. 13, compared with the
high-frequency filter 10 shown in FIG. 9, since the distance between the
tip parts 22a, 22b of the two pattern electrodes 16a, 16b, the distance
between the two input-output electrodes 24a and 24b and so on become
narrow, it is possible to miniaturize even more.
FIG. 15 shows the frequency characteristics of the embodiment shown in FIG.
9 and the embodiment shown in FIG. 13. From the frequency characteristics
shown in FIG. 15, in the embodiment shown in FIG. 13, compared with the
embodiment shown in FIG. 9, attenuation poles are generated at both a high
frequency side and a low frequency side, so the frequency characteristic
is better.
Meanwhile, in each embodiment shown in FIG. 9 through FIG. 14, though the
dielectric .layers 28a, 28b and so on are used as the capacitors 26a and
26b connected between the two pattern electrodes 16a, 16b and the two
input-output electrodes 24a and 24b, a chip capacitor, a capacitor formed
by a gap capacitance or the like, may also be used as the capacitor. For
example, compared with the embodiment shown in FIG. 9, as shown in FIG.
16, as the capacitors 26a and 26b connected between the tip parts 22a, 22b
of the pattern electrodes 16a, 16b and the input-output electrodes 24a,
24b, chip capacitors are respectively used. Or, compared with the
embodiment shown in FIG. 9, as shown in FIG. 17, the tip parts 22a, 22b of
the pattern electrodes 16a, 16b and the input-output electrodes 24a, 24b
may be closely formed, so that a gap capacitance therebetween may be used
to form the capacitors 26a and 26b connected between the tip parts 22a,
22b of the pattern electrodes 16a, 16b and the input-output electrodes
24a, 24b.
Also, in each embodiment shown in FIG. 9 through FIG. 14, though the second
parts 20a and 20b of the pattern electrodes 16a and 16b are respectively
extended from the first parts 18a and 18b at an angle of 45 degrees, it is
sufficient to form the second parts 20a and 20b so as to cross each other,
so the second parts 20a and 20b may be formed at another angle. For
example, one angle may be 40 degrees and the other angle may be 50
degrees.
Furthermore, in each embodiment shown in FIG. 9 through FIG. 14, though
having two pattern electrodes, that is, two resonators of length
.lambda./4, the present invention can be applied to a high-frequency
filter having three or more pattern electrodes, that is, three or more
resonators of length .lambda./4. In this case, the second parts (the open
ends) in two adjoining pattern electrodes may be formed so as to cross
each other, and a dielectric layer may be formed between the overlapped
parts.
Also, in each embodiment shown in FIG. 9 through FIG. 14, though as
described each example has a substrate having a high dielectric constant,
the present invention is not limited to a high dielectric constant, in
view of the miniaturization in the line direction of the pattern
electrodes.
Furthermore, in each embodiment shown in FIG. 9 through FIG. 14, though as
described each example has resonators of length .lambda./4 having one end
connected to the earth electrode, the present invention is also applicable
to a high-frequency filter with each resonator of length .lambda./2 having
one end open.
Also, in each embodiment shown in FIG. 9 through FIG. 14, though one
dielectric substrate is used, the present invention is also applicable to
a triple plate high-frequency filter wherein plural dielectric layers and
so on are laminated and made uniform. In this case, since the coupling
between the pattern electrodes becomes strong, the present invention
becomes especially useful.
It will be apparent from the foregoing that, 10 while the present invention
has been described in detail and illustrated, these are only particular
illustrations and examples, and the present invention is not limited to
these. The spirit and scope of the present invention is limited only by
the appended claims.
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